Pure fluid amplifier having a stable undeflected power stream



March 17, 1970 P. BAU 3,500,852

PURE FLUID AMPLIFIER HAVIN STABLE UNDEFLECTED POWER STREAM Filed Feb.'2, 1968 INVENTOR PETER BQUE R ATTORNEYS United States Patent 3,500,852PURE FLUID AMPLIFIER HAVING A STABLE UNDIEFLECTED POWER STREAM PeterBauer, Germantown, Md., assignor to Bowles Engineering Corporation,Silver Spring, Md., a corporation of Maryland Filed Feb. 7, 1968, Ser.No. 703,659 Int. Cl. F15c 1/14 US. Cl. 137--81.5 15 Claims ABSTRACT OFTHE DISCLOSURE A pure fluid amplifier has at least one stable state inwhich its power stream is undefiected. The stable undefiected powerstream is formed from two parallel spaced streams issuing into theamplifier interaction region from two nozzles in sufliciently closeproximity that mutual entrainment between the streams greatly reducesthe pressure between the stream relative to the regions on the othersides of the streams and causes them to merge downstream of the nozzles,stabilizing in a central position regardless of the sidewall effects.The wall surface between the nozzles is blunt rather than streamlined toenhance initial separation of the streams and faster mutual entrainmentof fluid between the streams.

BACKGROUND OF THE INVENTION The present invention relates to pure fluidamplifiers having at least one stable state and more particularly to atechnique for providing a stable position for a power stream in a fluidamplifier without requiring a surface to which the stream may attach.

It is known to provide fluid amplifiers with stable states or conditionsby utilizing the boundary layer wall attachment phenomenon. Thisphenomenon is responsible for etfecting attachment of a fluid stream toa wall and results from the entrainment of fluid by the stream from thespace between the stream and the wall, thereby reducing the pressure andcausing the stream to be deflected toward and become attached to thewall. In pure fluid amplifiers utilizing this phenomenon, stable powerstream conditions are characterized by location of the amplifierinteraction region sidewalls, such that positions of the power streamintermediate the two sidewalls are considered unstable. It is possibleto design a pure fluid amplifier in which the interaction regionsdewalls are sufliciently removed from the power nozzle or divergesufficiently therefrom so that an unperturbed power stream issuing fromthe power nozzle will not lock-on to the sidewalls; rather, lock-on insuch an amplifier will be achieved only if some perturbation ordeflecting force acts on the power stream. However, devices such asthese are extremely sensitive to power stream noise, shock and vibrationwhereupon the deflected power stream position is rendered quiteunstable. Also, the lock-on is not very stable and minor changes in loadcause the streams to become detached.

In some applications of fluid amplifiers it is necessary to providepower stream stability for power stream positions not corresponding toattachment of the power stream to the sidewalls. For example, atri-stable pure fluid amplifier may have two stable states in which thepower stream attaches to one or the other of the respective sidewalls,and a third state for which no sidewall is available to providestability. Further, it is also desirable in many cases for proportionalpure fluid amplifiers to have a stable undefiected power stream which isnot substantially affected by noise, shock or vibration.

In my prior US. Patent No. 3,192,938 I disclose a device having anoval-shaped interaction chamber with which three outlet passagescommunicate at its downstream end. Two of the outlet passages receivedfluid when the power stream was locked-on to one or the other of thesidewalls respectively in the interaction region. The third outletpassage received fluid when the power stream was undefiected and issuedthrough the center of the interaction region. The problem with thisdevice was the sensitivity of the power stream to external perturbationssuch as produced by shock and noise that tended to deflect the powerstream and cause it to lock-on to one or the other sidewalls of theoval-shaped interaction region. In addition, fluctuations in powerstream pressure produced problems in that a predetermined power streampressure had to be maintained in order to prevent the power stream frombeing deflected merely by unintentional minute asymmetries within theinteraction region.

A subsequent attempt to achieve power stream stability by other thanboundary layer wall attachment techniques is exemplified by the US.Patent No. 3,181,545 to F. E. Murphy, Jr. In the Murphy pure fluidamplifier a foil or fin is placed downstream of the power nozzle in theinteraction region, the power stream locking on to the fin or air-foilin accordance with well-known aerodynamic principles to provide a stablecondition for the power stream without utilizing an interaction regionsidewall. Specifically, the power stream in the Murphy device followsthe stream line configuration on both sides of the symmetric foil,thereby changing the length of the flow path of fluid in the powerstream immediately adjacent the foil. This increases the velocity in thefluid immediately adjacent the foil surface and produces a concomitantdecrease in pressure therein. As a result of the pressure decrease influid at the foil surface on both sides of the foil, the power streamattached to the foil to provide a stable state for the amplifier. TheMurphy device provides stability for the power stream in positions otherthan power stream attachment to the sidewalls; however, this is achievedin the Murphy device at the expense of pressure recovery. Specifically,the presence of the foil in the path of the power stream tends toincrease turbulence in the power stream downstream of and adjacent thefoil and thereby reduces the efficiency of the pressure recovery of thedevice. In addition, the Murphy technique is not suitable forutilization in proportional type pure fluid amplifiers due to inherenthysteresis eiiects associated with power stream lockonto the fin orfoil. Specifically, a predetermined pressure differential is requiredacross the power stream of the Murphy device before lock-on to the foilcan be destroyed. However, pressure difierentials lower than thepredetermined pressure ditferential, when applied across a power streamwhich is initially in some position other than that in which it islocked-on to the foil, do not produce lock-on to the foil but ratherdeflect the stream relative thereto.

It is an object of the present invention to provide power streamstability in fluid amplifiers without utilizing boundary layer lock-ontechniques, wherein the power stream position is insensitive toenvironmental disturbances, and without sacrificing amplifier pressurerecovery.

It is another object of the present invention to provide an improvedtri-stable pure fluid amplifier in which two stable states are achievedby conventional boundary layer techniques and in which a third stablecondition is achieved by effectively producing a boundary layer bubblein free space.

It is still another object of the present invention to provide a purefluid amplifier of the proportional type in which the undefiectedposition of the power stream is insensitive to noise and otherextraneous disturbances.

SUMMARY OF THE INVENTION In accordance with the present invention a pairof parallel adjacent streams are issued into the upstream end of a fluidamplifier interaction region in sufliciently close proximity to producemutual entrainment of fluid between the two streams. The pressurebetween the streams is quite low and consequently the streams merge toform a single stable power stream which may be utilized in fluidamplifier switching configurations of the monostable, bistable ortri-stable type, or alternatively in a proportional type pure fluidamplifier. In the preferred disclosed embodiments of the presentinvention the two streams are issued from respective nozzlescommunicating with the upstream end of the interaction region, thenozzles being separated by a blunt wall surface. The space immediatelydownstream of the wall surface between the two power streams ispartially evacuated by the entrainment of fluid therefrom by both of thestreams so that the streams may be effectively drawn together. In effecteach stream performs the function of an interaction region sidewall forthe other stream, i.e., it defines a surface displaced from the otherstream from which fluid is evacuated to form a boundary layer bubble.Since the surface is also a flowing stream, evacuation of fluid frombetween the streams is highly eflicient and the lock-on of one stream tothe other is quite strong so that deflection of the joined stream doesnot produce separation of the streams downstream of their confluence.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed description of one specificembodiment thereof, especially when taken in conjunction with theaccompanying drawing, wherein:

FIGURE 1 is a plan view of a tri-stable element constructed inaccordance with the principles of the present invention; and

FIGURE 2 is a plan view of a proportional pure fluid amplifierconstructed in accordance with the principles of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURE 1 of theaccompanying drawings for a more complete understanding of the presentinvention, there is illustrated a pure fluid amplifier of theconventional boundary layer type. The passages, cavities and nozzlesrequired to form amplifier 10 are preferably etched, molded or otherwiseformed in a flat plate 11 which is sandwiched and sealed between a pairof flat plates 12 and 13 by any conventional means such as machinescrews or adhesives. A power nozzle 14 formed in plate 11 has a flowdivider 15 disposed within its throat. The upstream end of flow divider15 is substantially wedge or V-shaped in order to facilitate flow aroundthe sides of the divider. The sides of flow-divider 15 are substantiallyparallel and, in conjunction with respective inwardly converging sidesof nozzle 14, define distinct left and right nozzles 17, 19 adapted toissue two respective streams of fluid into interaction region 21 ofamplifier 10. The downstream end of flow divider 15 defines the upstreamend of interaction chamber 21 and is substantially flat and generallyperpendicular to the sides of flow divider 15.

In the particular embodiment illustrated in FIGURE 1, flow divider 15 iscentrally disposed within power nozzle 14 so that the two nozzles 17 and19 defined by flow divider 15 and the walls of power nozzle 14 aresubstantially identical in size and configuration. Left and rightsidewalls 23 and 25 of interaction region 21 are positioned sufficientlyproximate respective left and right nozzles 17 and 19 so that boundarylayer effects are developed between these sidewalls and the streamsissued by the respective nozzles. Communicating with interaction region21 through respective sidewalls 23 and 25 are a pair of left controlnozzles 27 and 29 and right control nozzles 31 and 33 respectively. Thecontrol nozzles are adapted to receive respective control signals fordeflecting the resultant power stream issued from power nozzles 17 and19. l

Communicating with the downstream end of interaction region 21 is a leftoutput passage 35 adapted to receive resultant power stream fluid whenthe power stream attaches to left sidewall 23, a right output passage 39adapted to receive the resultant power stream when it attaches to rightsidewall 25, and a central output passage 37 disposed between passages35 and 39 and adapted to receive the resultant power stream whendirected generally centrally of interaction region 21. Left and rightvent passages 41 and 43 communicate with left and right output passages35 and 39 respectively and serve in a conventional manner to preventbackloading of either of passages 35 or 39 from causing switching of thepower stream.

A flow splitter 45 is positioned between left output passage 35 andcentral output passage 37; another flow splitter 47 is positionedbetween right output passage 39 and central output passage 37. Theupstream ends of flow splitters 45 and 47 are concave, forming cuspswhich act to peel off a portion of the fluid flowing into any of theoutput passages. The peeling ofi of fluid creates a vertical flow whichis fed back and stabilizes the power stream when directed toward therespective output passages in the manner fully described in US. PatentNo. 3,225,780 to R. W. Warren et al.

In operation, the application of pressurized fluid to nozzle 14 resultsin the issuance of two power streams from respective left and rightpower nozzles 17 and 19 into interaction region 21. These two powerstreams merge some distance downstream of flow divider 15 due to mutualentrainment between the streams by evacnation of the fluid between them.As a result of the forces acting to draw the streams together, themerged single stream achieves a stable position in which it is directedcentrally of interaction region 21 and out through central outputpassage 37. The flatness or bluntness of the downstream end of flowdivider 15 is instrumental in creating the desired stability of theresultant power stream in its central position since it partiallydefines a volume immediately downstream of the flow divider 15 betweenthe two streams from which the two streams mutually evacuate fluid. Tothis extent it is important that the downstream end of flow divider 15be blunt as opposed to streamlined, the latter configuration servingonly to merge two streams but not producing the evacuated space whichdraws the streams together rather than permitting each stream to beattracted to its adjacent sidewall. It is well known that a power streamissuing into an interaction region with sidewalls would be deflectedtoward one of the sidewalls. This tendency must be overcome in atri-stable device and is overcome in the device of the present inventionby creating a boundary layer bubble between the two streams having apressure, due to entrainment from both sides, less than the pressure onthe outside of the two streams.

The stability of the resultant power stream when directed toward centraloutput passage 37 is relatively insensitive to pressure variations inthe fluid supply nozzle 14 and to shock and vibration experienced in anormal operating environment. The stream in its central position is,however, somewhat more susceptible to deflection by a control signalapplied to one of the various control nozzles 27, 29, 31, 33, than isthe stream when attached to one of the interaction region sidewalls 23and 25; that is, there is no boundary layer lock-on to a fixed surfaceto be overcome by the control signal when the power stream is stablydirected toward central output passage 37.

For a device proportioned substantially as illustrated in FIGURE 1, thetwo power streams from nozzles 17 and 19 initially merge to form astable power stream directed to central output passage 37, assuming thatthere is no control signal applied to any of control nozzles 27, 29, 31and 33. If the combined resultant pressure of the control signalsapplied to the control nozzles is greater on one side of the resultantstream than the other, for example as would be the case if a controlsignal were applied to left control nozzle 27 and none of the othercontrol nozzles, the resultant power stream is deflected appropriately,in this case toward right sidewall 25 to which it attaches and isreceived by right output passage 39. Removal of the signal from controlnozzle 27 and application of a subsequent control signal to one of theright control nozzles 31 .or 33, at a sufficient pressure to overcomethe boundary layer effects causing attachment of the resultant stream toright sidewall 25, deflects the resultant power stream not to centraloutput passage 37, but to left output passage 35; that is, for theconfiguration illustrated in FIGURE 1 the boundary layer effect producedbetween the resultant stream and the left sidewall 23 is sufficient todeflect the power stream past the central output passage 37. Similarly,once the resultant power stream is attached to left sidewall 23,application of a control signal at a pressure suflicient to overcomelock-on to left wall 23 causes deflection of the resultant stream toright output passage 39, the resultant stream attaching to the rightsidewall 25. Once the resultant stream has attached to either sidewall23 or 25 it can readily be returned to its stable position directedtowards central output passage 37 only by equal pressures applied acrossthe resultant power stream.

Of course the above described operation can be modified somewhat bychanging the configuration of amplifier as desired. Specifically, if itis desired that the power stream be returned to its centrally stableposition from a deflected position by one control signal withoutrequiring equal and opposite control signals, modifications in thesidewall configurations can be provided. For example the sidewalls 23and 25 can be rendered more divergent than illustrated in FIGURE 1whereby to reduce the effectiveness of the deflecting force of theboundary layer phenomenon and thereby permitting the stream to beeffectively stepped from the left to central to right output passages orvice versa by a series of respective applied control pulses. A similarresult may be achieved by shortening the length of interaction region21; that is by moving flow splitters 45 and 47 somewhat closer to powernozzle 14. It will be evident in view of these remarks therefore thatvarious suitable configurations for tristable element 10 may be employedto produce the operation desired.

Amplifier 10 may be provided with a fourth stable state by providing acontrol port in communication with interaction region 21 through coverplate 12. This additional control port, positioned immediatelydownstream of divider 15, would be capable of introducing an additionalcontrol stream in the evacuated region between the two power streams soas to split the two power streams and cause them to attach to respectiveopposing sidewalls 23, 25 of interaction region 21. Depending on theconfiguration of these sidewalls, as discussed above, the split powerstreams may either remain attached thereto or rejoin upon removal of theadditional contfol stream. It the sidewalls 23 and 25 are configured sothat the split streams remain attached thereto after the additionalcontrol signal is removed, a fourth stable state is achievable which ischaracterized by simultaneous flow in output passages 35 and 39 and noflow in output passage 37. The stable split streams may be rejoined byapplying a control signal to any of control nozzles 27, 29, 31 and 33.It is to be recognized of course that the fourth stable state .of thepower stream (when it is split to flow in passages 35 and 39) ischaracterized by lower output pressure signals at passages 35 and 39than are present when the entire merged stream is deflected toward thesepassages.

Referring now to FIGURE 2 of the drawings, there is illustrated aproportional pure fluid amplifier 50 of the stream interaction type.Amplifier 50 is formed in two or three flat plates 51, 52 and 53, or anyother configuration for sealing the various passages, cavities andnozzles necessary for a fluid amplifier. Amplifier 50 includes a powernozzle 54 having a flow divider 55, substantially identical to flowdivider 15 of amplifier 10 in FIGURE 1, positioned therein to defineleft and right power nozzles 57 and 59 with respective left and rightsidewalls of nozzle 54. Power nozzles 57 and 59 are adapted to issueparallel pressurized streams of fluid into interaction region 61 fromthe upstream end thereof, the downstream end of divider 55 defining theupstream end of interaction region 61. The left and right sidewalls 63and 65 of the interaction region 61 are curved away from the orifices ofnozzles 57 and 59 so that no boundary layer effects will develop betweenthe power stream and these walls. A pair of left control nozzles 67 and69 and a pair of right control nozzles 71 and 73 are angularly disposedwith respect to the power nozzles 57 and 59 for effecting displacementof the power stream issued therefrom upon application of a controlsignal to the control nozzle at a sufiicient pressure. Three outputpassages 75, 77 and 79 communicate from left to right respectively withthe downstream end of interaction region 61. The downstream ends ofrecessed sidewalls 63 and 65 respectively communicate with respectivevent passages 81 and 83 formed through plate 52 to provide ambientpressure within interaction region 61 and thereby assuring that boundarylayer eflfects will not interfere with proportional operation of theamplifier 50.

As described previously in relation to flow divider 15 of amplifier 10,the presence of flow divider 55 in nozzle 54 produces a pair of parallelpower streams, which, when issued into interaction region 61, evacuatefluid from the region therebetween immediately downstream of divider 55and merge to form a single stable power stream directed centrally ofinteraction region 61 and towards output passage 77. As is well known inthe fluid amplifier art, output passage 77 may either be vented orconnected to a suitable utilization device; however, for purposes of thepresent discussion it will be assumed that output passage 77 is ventedand that the differential pressure signal appearing across left andright output passages 75 and 79 is the output signal of interest. Inaddition, any of control nozzles 67, 69, 71, 73 may be connected toreceive a respective input control signal for deflection of the mergedpower stream. However, for purposes of the present discussion it will beassumed that left control nozzle 69 and right control nozzle 73 arevented to improve the gain of amplifier 50 (as disclosed in US. PatentNo. 3,275,013 to John R. Colston) and that appropriate input signals areapplied to left control nozzle 67 and right control nozzle 71. In theabsence of any differential pressure appearing across nozzles 67 and 71,the merged power stream issues from vent output passage 77. The positionof the merged power stream is quite stable under these conditions, and,due to the forces which tend to draw the two individual streams issuedfrom nozzles 57 and 59 together, the merged stream is relativelyinsensitive to environmental shock, vibration, and noise. Application ofa control signal to control nozzle 67 acts to deflect the merged powerstream towards output passage 79, the degree of deflection of the mergedpower stream depending upon the pressure level in the signal applied tocontrol nozzle 67. Similarly a control signal applied to right controlnozzle 71 acts to deflect the merged power stream as a function of thesignal applied thereto. Thus the overall dilferential pressure appliedacross control nozzles 67 and 71 produces a resultant deflection of themerged power stream which is manifested by a pressure differentialappearing across left and right output passages 75 and 79. In thisrespect the amplifier 50 operates in a manner quite analogous to priorart proportional fluid amplifiers such as that disclosed in theaforementioned Colston patent. The difference in this proportionalamplifier 50, however, resides in the fact that the power stream issubstantially more stable and less sensitive to incidental disturbancesin its quiescent or undeflected position than is the case in prior artproportional fluid amplifiers. It is clear then that by utilizing theprinciples of the present invention a proportional pure fluid amplifiercan be provided wherein the output signal reflects a function of theinput signal with a high degree of accuracy because of the minimizationof internally generated noise.

It is to be understood that the configurations illustrated in FIGURES 1and 2, namely amplifiers 10 and 50, respectively are simply illustrativeof the principle underlying the present invention; namely theutilization of a pair of parallel adjacent power streams to form asingle stable power stream. Thus the use of a flow divider positionedwithin a nozzle is not to be construed as limiting since it is evidentthat a pair of completely independent adjacent power nozzles may beutilized to issue two parallel power streams which merge to form asingle stable stream. The advantage of placing the flow dividercentrally in nozzle resides in the fact that application of equalpressures to both adjacent nozzles is assured and therefore the singlepower stream can readily be issued centrally of an interaction region.However, for some applications it may be desirable to have independentnozzles and further, it may be desirable to produce a stable powerstream position other than centrally of the interaction region of theamplifier. The latter feature, of course, may be achieved not onlythrough utilization of independent nozzles, but also through positioninga flow divider in a nozzle such that adjacent nozzles of unequalcross-section are formed, whereby the stream issued from the nozzle oflarger cross-section tends to draw the other stream towards it ratherthan itself being drawn towards the stream issued from the smallernozzle. By this technique it may be seen that the resultant mergedstream may be issued in a stable configuration other than centrally ofthe interaction region.

In addition to the various configurations of the adjacent nozzlesdescribed in the preceding paragraph it is also important to understandthat the present invention is not limited to a tri-stable orproportional fluid amplifier as specifically illustrated in thedrawings. For example, amplifier 10 of FIGURE 1 may have one of itssidewalls, for example left sidewall 23, recessed to eliminate boundarylayer effects whereby the only two stable states for amplifier 10 wouldcorrespond to the power stream being directed toward right outputpassage 39 and central output passage 37 respectively. Likewise boundarylayer effects may be entirely dispensed with, as in the case ofamplifier 50 of FIGURE 2, and the left and right output passages ventedso that only variations of the power stream from its central positionare monitored at output passage 77. Further, both amplifier 10 andamplifier 50 may have their central output passages 37 and 77,respectively, removed and only a single flow divider or flow splitterprovided between the left and right output passages such that thecentrally stable position of the power stream provides equal flow to theleft and right output passages. Of course, variations of this two outputpassage device are conceivable in accordance with the present invention.

Still further, it is to be recognized that the two merging streamsprovided in accordance with the present invention need not be preciselyparallel. More particularly, it is possible to produce an evacuatedregion between the two streams when they are arranged at some smallangle relative to one another. Such streams would then be substantiallyparallel for purposes of the present invention.

The angle between the streams however should not be large enough topermit deflection of either stream due to momentum interchange; that is,the primary mechanism by which the two streams merge to form a singlestream should be the mutual entrainment between the streams.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variation of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the spirit and scope of theinvention.

What is claimed is:

1. A pure fluid amplifier having an interaction region, means forestablishing a power stream of fluid directed across said interactionregion, at least one output passage communicating with the downstreamend of said interaction region for selectively receiving said powerstream, and means for selectively deflecting said power stream in saidinteraction region relative to said output passage, said amplifier beingcharacterized in that said means for establishing a power streamcomprises means for issuing two substantially parallel fluid streamsinto the upstream end of said interaction region, said streams beinglocated such as to define an evacuated region between said streams tocause said streams to be deflected toward one another and mergedownstream of said evacuated region to form a single stable powerstream.

2. A pure fluid amplifier according to claim 1 wherein said means forissuing comprises a pair of nozzles, each nozzle having an egressorifice communicating with the upstream end of said interaction region,said egress orifices being separated by a substantially blunt surface.

3. The combination according to claim 2 wherein said pair of nozzles areformed from a single nozzle having a throat with a flow divider disposedtherein.

4. The pure fluid amplifier according to claim 1 wherein said amplifieris a tri-stable pure fluid device, said interaction region being definedby a pair of sidewalls which are sufliciently close to said singlestable power stream to produce boundary layer elfects between saidsidewalls and said power stream, said at least one output passage beingdisposed to receive said single stable power stream when undeflected,and further comprising two additional output passages disposedrespectively to receive said single power stream when the latter isattached to respective ones of said sidewalls.

5. A pure fluid amplifier according to claim 4 wherein said means forissuing comprises a pair of nozzles, each nozzle having an egressorifice communicating with the upstream end of said interaction region,said egress orifices being separated by a substantially blunt surface.

6. The combination according to claim 5 wherein said pair of nozzles areformed from a single nozzle having a throat with a flow divider disposedtherein.

7. The combination according to claim 6 wherein said flow divider has anapex at its upstream end and converges in a downstream direction.

8. The combination according to claim 6 wherein said pair of nozzleshave equal cross-sectional areas.

9. The combination according to claim 1 wherein said pure fluidamplifier is a proportional amplifier in which said interaction regionhas sidewalls sufliciently displaced from said single stable powerstream to prevent boundary layer effects from deflecting said singlestable power stream toward said sidewalls, whereby said single stablepower stream is stable only in its undeflected position.

10. The combination according to claim 9 wherein is further provided asecond output passage, said at least one and said second output passagesbeing disposed to provide a differential pressure output signal as afunction of the deflection of said power stream.

11. The combination according to claim 1 wherein is further provided asecond output passage, said at least one and said second output passagesbeing disposed to provide a differential pressure output signal as afunction of the deflection of said power stream.

12. A pure fluid amplifier having an interaction region with an upstreamend and a downstream end, at least one outlet passage communicating withsaid interaction region at said downstream end, source means for issuinga pair of substantially parallel fluid streams into said interactionregion at said upstream end, said fluid streams being sufficientlyproximate one another to define a low pressure region therebetween fromwhich both streams entrain fluid and toward which both streams aredeflected sufficiently to merge into a single deflectable power stream,the proximity of said streams being sufliciently close to maintain saidfluid streams so merged for any and all deflected positions of saidpower stream.

13. The pure fluid amplifier according to claim 12 wherein said sourcemeans comprises a pair of spaced nozzles arranged to issue said fluidstreams into said upstream end, said nozzles being separated by a bluntsur face defining the upstream boundary of said low pressure region.

14. The pure fluid amplifier according to claim 13 wherein saidinteraction region includes opposite sidewalls which are sufficientlydisplaced from said power stream to prevent boundary layer eflectsbetween said power stream and sidewalls from deflecting said powerstream toward said sidewalls.

15. The pure fluid amplifier according to claim 13 wherein saidinteraction region includes at least one sidewall positionedsufficiently proximate said power stream to cause boundary layer effectsbetween said power stream and at least one sidewall to enhance anydeflection of said power stream toward said one sidewall.

References Cited UNITED STATES PATENTS 3,080,886 3/1963 Severson 13781.53,181,545 5/1965 Murphy 13781.5 3,366,131 1/1968 Swartz 137-81.53,413,994 12/1968 Sowers 137-815 3,416,487 12/1968 Greene -137 81.5X

M. CARY NELSON, Primary Examiner WILLIAM CLINE, Assistant Examiner

